In the demolition of buildings and other structures, crushing of concrete is generally carried out using a chisel (teeth) device which is opened and closed by a hydraulic jack. Known as a concrete crusher, this device comprises a pair of jaws for biting concrete as secured to the free end of the driving arm of a construction machine, typically a power shovel, a hydraulic cylinder for opening and closing said jaws, and chisel or crushing means attached to the mating faces of the jaws.
In order that the crushing capacity of such a concrete crusher may be increased, it is important to insure that the output of the hydraulic cylinder will act on the crushing chisel means as a concentrated load and also that, in consideration of the fact that concrete is rather resistant to compressive forces, the crushing force will act not as a compressive force but as a bending moment. Several proposals have been made in accordance with the above deign concepts.
For example, it was proposed to provide the mating faces of a pair of jaws with crushing means each comprising a plurality of projecting bars arranged in parallel with a pivot pin but in staggered relation between the jaws so that the output of a hydraulic cylinder may act as a concentrated load and, at the same time, exert bending moments on the concrete (Japanese Patent Publication No. 58-14909).
It was also proposed to provide a pair of jaws, with the lower jaw having on its mating face a plurality of longitudinal cutters arranged in the form of a fork and perpendicular to a jaw pivot pin and a plurality of auxiliary cutters as arranged between said longitudinal cutters and perpendicular to the latter to constitute a grate-like cutter system, while the upper jaw is provided on its mating surface with a large sharp-pointed rough crushing cutter perpendicular to said pivot pin and a plurality of sharp-pointed cutters (chisels) directed against said grate-like cutting system of the lower jaw. In this arrangement, a concentrated load is applied to the large rough crushing cutter to rough-cut the concrete in the first place and, then, bending moments are applied to the concrete by means of the grate-like cutting system of the lower jaw and the chisels of the upper jaw (Japanese Patent Publication No. 1-27504).
It has also been proposed to provide a concrete crusher such that, in the crusher arrangement proposed in said Japanese Patent Publication No. 1-27504, said large rough-cutting tool is omitted and, instead, the upper jaw is provided with a multiplicity of chisels corresponding to the meshwork of the grate-like cutting system of the lower jaw (Japanese Kokai Patent Application No. 60-113258, Japanese Utility Model Publication No. 61-28839).
However, in all of the crashers referred to above, the cutters are arranged in staggered relation so that bending moments may act on the concrete to achieve an improved crushing effect but the crushing cutters tend to be worn rapidly just because they act to produce bending moments and particularly if the cutters are chisels, they must be replaced at short intervals.